Molecular characterization of P-29, a metacestode-specific component of Echinococcus granulosus which is immunologically related to, but distinct from, antigen 5

In this work the characterization of P-29, a novel 29 kDa antigen from Echi nococcus granulosus is reported. E. granulosus was identified while looking for parasite antigens distinct from those present in hydatid cyst fluid. A monoclonal antibody (mAb 47H.PS) prepared against protoscolex components r evealed that P-29 is localized to the tegument and rostellum of protoscolec es, and to the germinal layer of the cyst, but it is absent in hydatid cyst fluid or adult worm extracts. Several internal fragments of P-29 showed se quence identity to the amino acid sequence encoded by Eg6, a partial gene s equence reported to code for an epitope of antigen 5 (Ag5), one of the majo r diagnostic antigens of the parasite. We confirmed that Eg6 encodes a sub- fragment of P-29 by mapping the epitope of mAb 47H.PS, and isolating the fu ll length P-29 cDNA. Since Eg6 had been postulated to encode a fragment of Ag5, we specifically studied the relationship of P-29 and Ag5 by: (i) exami ning the cross-reactivity displayed by different mAbs; (ii) comparison of t heir peptide finger prints; and (iii) a comparative study of their diagnost ic value. Our results prove unequivocally that P-29 and Ag5 are immunologic ally related, but different proteins, raising several questions on the curr ent knowledge of Ag5. (C) 2000 Elsevier Science B.V, All rights reserved.